One two three four channel guitar amplifiers
Most amps have more than one channel. Personally I use a one trick pony. That means I have an amp on witch I can only use one channel at a time. No switching possibilities. For different sounds I use effect pedals.
Most guitarists prefer an amplifier with more selectable channels.
An amp with more channels gives you the possibility to switch between different amp settings. The switching can be done by a foot switch.
One channel for a nice clean tone. On another a little more crunch and one more for a good lead tone.
On a modeling amp you have lots of possibilities for different sounds.